The invention relates to dynamoelectric machines of the type having permanent magnets positioned in the field poles thereof. More particularly, the invention relates to dynamoelectric machine field poles having rare earth magnets with relatively high coercive forces mounted in novel, pre-cured magnet sub-assemblies that are then assembled into a unique pole construction. The invention also relates to a method for manufacturing such magnet sub-assemblies and field poles.
In the manufacture of dynamoelectric machines it has long been a known practice to improve the magnetic characteristics of field poles for such machines by inserting permanent magnets into their magnetic flux paths. An early example of such use of permanent magnets is shown in U.S. Pat. No. 1,485,393 which illustrates a motor having field poles with permanent magnets mounted, respectively, at the base of each pole. As the development of such permanent magnet pole structures progressed, a number of improvements were introduced. For example, in U.S. Pat. No. 2,193,406 there is shown a pole structure in which the pole laminae are welded together to rigidify the poles and each of the poles is made longer than the machine core to improve the magnetic characteristics of the machine. In order to adjust the magnetic reluctance of various field pole arrangements, it also became common to provide shims or movable bolts for adjusting the relunctance of the field circuits. For example, U.S. Pat. No. 3,441,760 shows the use of such shims and U.S. Pat. Nos. 3,214,620 and 3,562,568 illustrate the use of adjustable bolts in dynamoelectric machines to adjust the magnetic characteristics thereof.
In more recent times the substitution of rare earth magnets, such as those made of cobalt-samariam for the earlier used Alnico and ceramic types of magnets in such field pole constructions, has become more feasible. Such rare earth permanent magnets are particularly advantageous in the manufacture of dynamoelectric machines because their high coercivity, i.e., their resistance to demagnetization, and good magnetic induction are now available at reasonable cost. Due to the high coercivity of rare earth permanent magnets, magnet length can be reduced about an order of magnitude further or can be reduced to about 10% of the length of Alnico magnets. It is often possible in the manufacture of permanent magnet dynamoelectric machines utilizing such magnets to eliminate the need for pole shoes; thus, the rotor size of the machines can be increased. With such increased rotor sizes numerous advantages are realized such as increased heat dissipation and the ability to add slots into the rotors thereby increasing the number of ampere turns, which results in proportional increases in the torque that can be developed by a machine having a given outside diameter. Alternatively, by the use of such rare earth permanent magnets, it is possible to reduce the size of a given horsepower motor relative to the size that would have previously been needed to accommodate more conventional permanent magnet pole constructions.
In the manufacture of relatively small permanent magnet d.c. motors it is known to use plate-shaped permanent magnets directly adhered to the surface of a motor housing to support pairs of such magnets in operating relationship against a common pole shoe that partially encompasses a rotor of the machine. It is also relatively common practice to provide slots in such common pole shoes in order to reduce the flux shifting in the shoes as a result of armature crossfields. Examples of such known prior art structures are illustrated in U.S. Pat. No. 3,296,471 which issued on Jan. 3, 1967. As is suggested in that patent and as is more clearly explained in U.S. Pat. No. 3,590,293, which issued on June 29, 1971 and is assigned to the assignee of the present invention, it is a well-known practice to mount permanent magnets in a dynamoelectric machine by adhering the magnets to a mounting surface with an epoxy resin or other suitable glue.
While many of the foregoing prior art methods are useful in the manufacture of relatively small permanent magnet dynamoelectric machines, it is also desirable to improve the response time and reduce the manufacturing costs of larger machines that utilize laminated, salient field poles. Thus, it would be desirable to provide means for mounting high coercive forces, rare earth magnet assemblies into laminated field poles of a d.c. machine in a manner that optimizes the magnetic characteristics of the poles while reducing the overall weight of the machine required to produce a given torque or horsepower.
It is a primary object of the present invention to provide a permanent magnet dynamoelectric machine having field poles that incorporate rare earth magnet sub-assemblies in an optimum relationship that improves the magnetic characteristics of the poles while reducing the overall pole size required to develop a given magnetic flux at the air gap between the poles and the rotor.
Another object of the invention is to provide a permanent magnet pole for a dynamoelectric machine in which a plurality of permanent magnets in bar form are arranged in a predetermined package configuration including sheets of magnetic material cemented to the magnets which are subsequently arranged between laminated pole base and pole face members before being fixed in relation thereto by a mounting means.
Yet another object of the invention is to provide a permanent magnet field pole for a dynamoelectric machine in which a rigid pole base member supports a relatively more flexible pole face member and rare earth magnet sub-assemblies sandwiched between the pole face and base members.
Still another object of the invention is to provide a method for manufacturing a permanent magnet pole structure for a dynamoelectric machine in which the pole structure has a rigid base member and a relatively more flexible face member.
A further object of the invention is to provide a method for making a permanent magnet dynamoelectric machine pole structure in which rare earth magnet sub-assemblies are preformed and adhered together with a partially cured adhesive before magnetizing flux is applied to the sub-assembly to polarize the magnets therein.
Additional objects and advantages of the invention will be apparent from the description of it presented herein taken in conjunction with the accompanying drawings.